Doctor blade for controlling bulk density of dehydrated cereal products

ABSTRACT

An improvement for a film type, rotary drum drier for controlling the bulk density of high sugar content dehydrated cereal products discharged from the drum drier by a doctor blade at a given angle of attack with respect to the surface of the drum drier is disclosed which comprises shaping the doctor blade substantially as showed in FIG. 4.

O United States Patent 1191 3,7 Hyldon Jan. 15, 1974 [54] DOCTOR BLADE FOR CONTROLLING 3,014,833 12/1961 Lee 15/256.51 x BULK DE S 0 DEHYDRATED 3,494,050 2/1970 Wadsworth et a1. 159/1 1 R X 3,577,649 5/1971 Wadsworth 34/110 CEREAL CT 3,592,667 7/1971 Kelly et a1 159/1 1 R X [75] Inventor: Roy G. I-Iyldon, Crystal Lake, Ill. 3,642,536 9 2 5/256-5l X 3,611,841 101971 F d ..76101R [73] Assignee: The Quaker Oats Company, l to en Chicago, 111. FOREIGN PATENTS OR APPLICATIONS 978,988 1/1965 Great Britain l5/256.51 [22] Wed? June 1972 792,883 1/1936 France 144/212 [21] Appl. No.: 267,484

Primary Examiner-Jack Sofer 52 11.s.c1 159/11, 99/207, 15/256.51, ArwrneyGrae Fishel er 34/110 [51] Int. Cl BOld 1/22, A23b 7/03, F26b 11/02, [57] ABSTRACT A231 1/12, A46b 15/00 1 58 Field of Search 34/110, 113, 114, An Improvement for a film yp rotary drum drier for 34/115, 122, 127, 130, 131, 132, 240; controlling the bulk density of high sugar content de- 5 5 5 25 5; 144/115 5 7 hydrated cereal products discharged from the drum 99 /1 70, 242 drier by a doctor bladeat a given angle of attack with respect to the surface of the drum drier is disclosed 5 References Cited which comprises shaping the doctor blade substan- UNITED STATES PATENTS tially as showed in FIG. 4. p

2,570,845 10/1951 Ottersland 144/212 X 2 Claims, 7 Drawing Figures END 6|BOARD GAS TO PREVENT 2 FLOWOUT PATENTED JAN 1 51974 sum 1 or z END OARD DOCTOR BLADE FOR CONTROLLING BULK DENSITY OF DEHYDRATED CEREAL PRODUCTS BACKGROUND OF THE INVENTION 1. Field of the Invention" This invention relates to an improvement in a doctor blade for a film type, rotary drum concentrating evaporator. More particularly, this invention relates to an improvement in a doctor blade for a rotating double-drum drier. v

2. Description of the Prior Art Drum drying involves the application of a liquid material such as a solution, slurry or paste to the exterior of a revolving heated drum. As the drum rotates, the heat of the drum dries the thin sheet of material by reducing the water content thereof through evaporation. The dried material is scraped from the exterior surface of the drum by a doctor blade spaced around the drum periphery from the point of application of the liquid material a distance corresponding to that desired to allow for drying.

In the cereal industry, drum drying is usually accomplished with atmospheric double-drum driers, i.e., a pair of closely spaced cylindrical drying surfaces that are heated internally as by steam. Drums are conventionally employed that have the same radius and are in parallel alignment with their axis of rotation on the same level. The cereal slurry to be dried is disposed as a puddle in the trough formed between the upper, adja cent surfaces of the two drums. Endboards or gas discharging means set to direct a gas toward the middle of the drums are employed to confine the liquid between the drums. The puddle, normally in direct contact with the upper adjacent surfaces of both drums, provides a thin film that is deposited on the drums as they rotate downwardly toward the nip formed between their adjacent outer surfaces. Drying of the film continues throughout the rotation of the drum prior to being scraped from each 'drum by respective doctor blades.

In U. S. Pat. No., 3,577,649 it is demonstrated that by varying the angle of attack of the doctor blade with respect to the surface of the drum drier that the bulk density of a dried sheet having a high sugar content can be varied. This is due to a ruffling effect which occurs as the dry, hot, thermoplastic material is scraped from the drum by the doctor blade. The doctor blades used as abovedescribed have heretofore had one deficiency. Customarily the doctor blade is sharpened to an edge. As the blade wears in contact with the drum the leading edge of the blade becomes blunted in a manner which causes an unacceptable greater ruffling effect and hence a sheet having a higher bulk density.

To counteract the blunting of the doctor blade the angle of attack of the doctor blade with respect to the surface of the drum drier must be reduced. Reducing the angle reduces the degree of ruffling and hence the bulk density of the high sugar content cereal product. To reduce the angle of the doctor blade, the doctor blade holder must be pivotally held in place by an adjustable holder support. While adjustable holder supports are available in the art, they are expensive and bothersome to adjust during the drying operation.

SUMMARY OF THE-INVENTION Accordingly, the principal object of the present invention is to provide a doctor blade for a drum drier whose angle with respect to the drier does not have to be adjusted during the drying operation to maintain a substantially constant bulk density of the product Other objects will be apparent to one skilled in the art in view of the following description of the invention.

The objects of this invention are accomplished in a drum drying apparatus for drying cereal products of high sugar content comprising, in combination, a rotatable elongated drying drum associated stationary front and side supporting structure for said drum, said drum being mounted between said stationary support members for rotation about its longitudinal axis, and a doctor blade for scraping dried cereal product from said drum by the improvement which comprises a doctor blade having one side thereof beveled to a point and then squared to provide a scraping edge. By high sugar content I mean a sugar content of at least 25 percent by weight (dry weight basis).

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view of the apparatus of the invention.

FIG. 2 is a sectional view of the apparatus taken along the line 2-2 of FIG. 1.

FIG. 3 is a side view of the doctor blade of this invention.

FIG. 4 is a side view of the doctor blade of this inventron.

FIG. 5 is a side view of the doctor blade of this invention after it has become worn.

FIG. 6 is a side view of a prior art doctor blade.

FIG. 7 is a side view of a priorart doctor blade after it has become worn.

In FIG. 1 there are shown rotatable drums 12 and 13. Axles l4 and 15 are attached to drum 13 and used to support drum 13. Axles 16 and 17 are attached to drum l2 and used to support drum 12. Drum 13 is heated by a steam inlet pipe 18 which extends into the drum, and the steam condensate is then removed from drum 13 by condensate pipe 19 which extends into the drum and into the condensate collection within the drum. Drum 12 is heated by steam inlet pipe 22 which extends into the drum, and the steam condensate is in turn removed by condensate pipe 23 which extends into the condensate in the drum. The axles l4} and 15 of drum 13 are supported by the housing units 24 and 25 respectively. The housing unit 24 is attached to a spring loaded mounting 26. The housing unit 25 is supported by a spring loaded mounting 21. The axles 16 and 17 of drum 12 are supported by the housing units 27 and 28 respectively. The housing units 27 and 28 are supported on spring loaded mountings 23 and 32 respectively. The drums 12 and 13rotate in opposite directions such that the tangential motion of both drums at the point at which they are closest to each other is in the downward direction. The sugar containing slurried material 34 falls into the trough 35 between the drums l2 and 13. The rotation of the drums forces the sugar containing slurried material 34 into the nip 36 between the drums. At this point, the slurried material 34 forms the thin sheets of material 37 and 38 on drums 12 and 13 respectively. The end board 61 has a gaseous supply line 62 coming to it and extendingthrough it. The gaseous substance is discharged through nozzle 63 at a rate to prevent the sugar containing slurried material 34 from following off the ends of drums 12 and 13. The doctor blades 39 and 40 remove the thin sheets 37 and 38 respectively from the drums l2 and 13.

In FIG. 2, there is shown a dryer drum 12, wherein the rotation of the drum as viewed would be clockwise and the dried material 37 adhered to the drum surface is scraped off by doctor blade 39, and discharged from the dryer in the form of a continuous sheet 37, which is supported by roller 41.

FIGS. 3 and 4 are illustrations of the doctor blade of this invention. The periphery of the dryer drum 12 is touched by the doctor blade 39 at the point of contact 42. The optimum location of the point of contact relative to the point of applying feed material to the drum surface depends upon the design of the dryer and the characteristics of the feed material. The plane T represents a surface tangent to the drum at line or element of contact 42. The angle a which affects the bulk density of the drum dried high sugar content materials is the dihedral angle which is formed by the intersection of plane T, which is tangent to the surface of the drum at the line of contact 42 with surface B which is coplanar with the beveled squared face of the doctor blade.

The angle a of attachment may be varied from about 30 to 165.

The width of the squared face of the doctor blade 44- is between 0.002 inch and 0.005 inch. In other embodiments of this invention the width of the squared face 44 of the doctor blade may be between 0.001 inch and 0.010 inch. The width of the beveled face B of the doctor blade 43 is customarily 0.50 inch but may be greater or lesser.

FIG. 5 is an illustration of the doctor blade of this invention identical to FIG. 4 except that the squared face 44 the doctor blade is shown as worn.

FIG. 6 is an illustration of a prior art doctor blade 59 used in place of the doctor blade of this invention 39 for purposes of comparison.

FIG. 7 is an illustration of a prior art doctor blade identical to that of FIG. 6 except that the edge of the blade has been blunted by use.

PRACTICAL OPERATION In operation, the drums l2 and 13 are rotated with their tangential motion at the point at which they most nearly meet being in the downward direction. The steam inlet pipes 18 and 22 convey steam to the drums l3 and 12 respectively to heat them. As the steam condenses, condensate pipes 19 and 23 remove the condensate from drums l3 and 12 respectively. The rate of rotation of the drum and the temperature to which the drums are heated by the steam depend upon the desired drying rate and allowable drying temperature for the material being dried. The slurried material 37 is discharged approximately midway between the ends of the drums. As the slurried material land .in the trough 35, it tends to spread out the entire length of the trough. As the slurried material approaches the ends of the drums, the flow rate of the gaseous material brought to the drier by gaseous supply lines 62 is adjusted to a rate sufficient to prevent the slurried material from exceeding the ends of the drums. As the drums rotate, the slurried material is forced into the nip 36 between the two drums. The spacing of the drums at the nip is adjusted to give the desired thickness of the thin sheet of material 45 which in turn affects the drying rate. The thin sheets of material adhere to the drums as the drums rotate, and the material is dried and/or cooked to the desired degree. After the thin sheets of material are sufiiciently cooked and dried, they are removed by doctor blades 39 and 40. The bulk density of the high sugar content cereal is determined by the angle a As the doctor blades 39 and 40 wear in contact with drums 12 and 13 respectively, the squared face 44 becomes worn but the impedance to the movement of the dried cereal across the doctor blade remains substantially constant. The bulk density of the high sugar content cereal, therefore, remains substantially constant.

The prior art differs from the above in the following respect: As the doctor blade 50 wears in contact with the drum 12 the impedance to the movement of the dried cereal across the doctor blade increases and therefore the bulk density of thehigh sugar content cereal increases. To maintain the bulk density of the product, the angle a must be increased so that the impedance is reduced.

Having fully described this new and novel invention,

I claim:

1. In a drum drying apparatus for drying cereal products of high sugar content comprising, in combination,

a rotatable elongated drying drum, associated stationary front and side supporting structure for said drum, said drum being mounted between said stationary support members for rotation about its longitudinal axis, and a doctor blade coextensive and in contact with the drum for scraping dried cereal product therefrom, the improvement which comprises said doctor blade having two parallel faces joined by a bevelled face and having its sharp edge blunted by being'square d off to provide a scraping surface perpendicular to that parallel face adjacent and contiguous to the drum, the width of said squared surface of the doctor blade being between 0.001 inch and 0.010 inch.

2. The doctor blade of claim 1 wherein the width of the squared face is between 0.002 inch and 0.005 inch. 

1. In a drum drying apparatus for drying cereal products of high sugar content comprising, in combination, a rotatable elongated drying drum, associated stationary front and side supporting structure for said drum, said drum being mounted between said stationary support members for rotation about its longitudinal axis, and a doctor blade coextensive and in contact with the drum for scraping dried cereal product therefrom, the improvement which comprises said doctor blade having two parallel faces joined by a bevelled face and having its sharp edge blunted by being squared off to provide a scraping surface perpendicular to that parallel face adjacent and contiguous to the drum, the width of said squared surface of the doctor blade being between 0.001 inch and 0.010 inch.
 2. The doctor blade of claim 1 wherein the width of the squared face is between 0.002 inch and 0.005 inch. 